The present invention relates to apparatus for counting the number of discharges through a voltage surge arrester and particularly to improved apparatus for counting only those surge arrester discharges having a significant effect on the arrester's useful life.
Typical surge arrester discharge counters respond to the flow of discharge current through the arrester and thus record each discharge event essentially without regard to the magnitude of the discharge energy. U.S. Pat. Nos. 3,443,223, 3,469,188, 4,112,418 and 4,338,648 exemplify this approach. Since the magnitude of the energy absorbed by the arrester incident with a surge discharge is the most significant debilitating factor insofar as arrester life is concerned, simply counting arrester discharges may not in many situations provide an accurate indication of an arrester's remaining useful life. That is, the discharge of a brief voltage spike having little associated energy will have negligible degrading effect on the varistor elements in the arrester, yet the discharge is counted when using the prior art discharge current sensing approach.
It is accordingly an object of the present invention to provide a more reliable approach to predicting the useful life span of a voltage surge arrester.
A further object of the present invention is to provide apparatus for counting only those surge arrester discharges exceeding a predetermined minimum energy content.
Another object is to provide surge arrester discharge counting apparatus of the above character which is convenient to implement and reliable in operation.
Other objects of the invention will in part be obvious and in part appear hereinafter.